Some of the automotive vehicles such as, for example, trucks travel a substantial total distance of more than a billion kilometer within the life cycle of such vehicles as compared with passenger cars. In the case of those automotive vehicles, the wheel support bearing assemblies employed therein are desired not only to have a correspondingly increased service life but also to employ bearing sealing devices of an increased life time, which are provided at opposite ends of an annular bearing space found in each of the wheel support bearing assemblies.
In view of the above, a bearing sealing device such as shown in FIG. 15, for example, designed to have an increased resistance to muddy water, has been suggested, which includes an L-sectioned sealing plate 62, fitted to a bearing inner ring and having a cylinder wall 62a and a radial upright wall 62b protruding radially outwardly from the cylinder wall 62a, and a core metal equipped elastic sealing member 63 fitted to a bearing outer ring and having two side sealing lips 63a and 63b slidingly engaged with the radial upright wall 62b of the sealing plate 62 and positioned one inside the other with respect to a radial direction thereof. (See, for example, the Patent Document 1 listed below.)
Another bearing sealing device 90, similarly designed to have an increased resistance to muddy water, has also been suggested as shown in FIG. 16, which makes use of rolling elements or balls 64 of a small diameter and in which opposite ends of a bearing space delimited between a bearing outer ring 71 and a bearing inner ring 72 are sealed by respective bearing sealing devices 61 each having side sealing lips 63a and 63b similar to those shown and described with reference to FIG. 15. (See, for example, the Patent Document 2 listed below.)    [Patent Document 1] JP Laid-open Patent Publication No. 2007-9938    [Patent Document 2] JP Laid-open Patent Publication No. 2001-165179
However, if the two side sealing lips 63a and 63b are provided in the bearing sealing device as hereinabove discussed, the resistance to muddy water may increase to a value about twice that exhibited by the conventional standard bearing sealing device, but considering the distance of travel of the trucks, a further increase of the resistance to muddy water is desired.
In addition, with the bearing sealing device of the structure utilizing the two side sealing lips 63a and 63b as discussed above, the widthwise dimension may fall within the range of 4.5 to 5.0 mm, but the sectional height of 8.5 to 10 mm is required and a problem has therefore been found that as compared with the bearing sealing device of the standard structure utilizing only one side sealing lip, the sectional height is large. Considering that in the field of automotive vehicles, low fuel consumption is increasingly desired in recent years, a bearing sealing device is desired of a structure that enables reduction in weight along with compactization not only in an axial direction, but also in a radial direction of a wheel support bearing assembly, where such bearing sealing device is to be incorporated in the wheel support bearing assembly for automotive vehicles. In order to meet such requirements, the bearing sealing device is desired, which is of a kind capable of increasing the resistance to muddy water and having a low sectional height.
In the conventional bearing sealing device utilizing the two side sealing lips, little care has been paid to the relation of the distance between the side sealing lips with the resistance to muddy water and the distance between the two side sealing lips has been equal to or smaller than 0.1 mm while the sectional height has been chosen 8 mm or higher. For this reason, with those dimensional conditions found in the conventional bearing sealing device now under discussion, little effort has been found leading to an improvement of the resistance to muddy water despite of the structure utilizing the two side sealing lips.
As discussed above, if the sectional height of the bearing sealing device can be reduced, it appears to be advantageous in terms of reduction in weight and size of the wheel support bearing assembly that utilized such bearing sealing device. However, as shown in, for example, FIG. 17, when the bearing sealing device is to be installed on an inboard side of a wheel support bearing assembly 100, which is a dual row outwardly oriented angular contact ball bearing of a third generation type, reduction of the sectional height of the bearing sealing device 81 may lead to a weight increase due to formation of a volume or weight increasing portion 91a in one (for example, an outer member 91) of bearing component parts depending on the specification of the bearing assembly. In other words, the outer diameter D of a portion of the outer member 91, positioned on the outer perimeter of the bearing sealing device 81, is a portion, that is to be mounted on a counterpart member such as, for example, a knuckle, and depends on such counterpart member. For that reason, if the sectional height of the bearing sealing device 81 is reduced, the inner diameter of that portion of the outer member 91, where the bearing sealing device 81 is mounted, becomes small, accompanied by increase of the wall thickness enough to form the weight increasing portion 91a. For this reason, where the bearing sealing device is to be reduced in section, care must be taken to avoid anything that hampers reduction in weight and compactization of the wheel support bearing assembly.